This invention relates generally to chemical mechanical polishing apparatuses and more particularly, it relates to a chemical mechanical polishing (CMP) apparatus for polishing a semiconductor wafer used in the fabrication of silicon-based semiconductor devices which includes a CMP platen plug for eliminating an air pocket bubble from forming underneath a polishing pad.
As is known to those skilled in the art of integrated circuit fabrication, the formation of integrated circuits is started initially with the production of high quality semiconductor wafers which are made from a silicon substrate or the like. The semiconductor wafers are usually sliced from ingots of various size dimensions. The slicing process and subsequent processing can cause surface damage to the semiconductor wafers and will result in wafers having variations in thickness and a rough surface. Since an extremely flat surface is desirable for further processing into semiconductor devices, it is generally known to subject the wafers to a polishing process, sometimes referred to as chemical mechanical polishing (CMP), so as to achieve such a flat surface. The polished wafer is generally required to be free from defects and be extremely flat when it is utilized in the fabrication of sub-micron semiconductor devices.
One conventional CMP apparatus for polishing a semiconductor wafer used in the fabrication of semiconductor integrated circuit devices is illustrated in FIG. 1 and is labeled "Prior Art." As can be seen, this conventional polishing apparatus 10 is similar to the type Avanti427 which is manufactured and sold by IPEC Planar of Phoenix, Ariz. The polishing apparatus 10 is housed and supported on a frame 12 which includes, among other things, a plurality of working stations formed of a cleaning station 14, a first or primary polishing station 16, and a secondary or final polishing station 18. For purposes of convenience, the other components not related to the present invention have been purposely omitted.
As is well-known in the art, a carrier or wafer-carrier head 20 is rotatably mounted on a polishing arm or spindle for moving a semiconductor wafer (not shown) from a pick-up station (also not shown) over the cleaning station 14. The semiconductor wafer is picked up from the pick-up station under a vacuum and is held to the bottom or underneath side of the wafer-carrier head 20 and is then moved to the cleaning station 14. The cleaning station 14 includes a trough 22 into which the wafer-carrier head 20 with the wafer is lowered and against a cleaning spray (not shown). Next, the semiconductor wafer is moved to the primary polishing station 16.
The primary polishing station 16 also includes a trough 24 in which is disposed a first metal polish platen 26 having a polishing pad 28 mounted on its top surface. For polishing, the wafer-carrier head with the wafer held on its bottom surface is forced downwardly against the polishing pad 28. During the time of polishing, no vacuum is used to support the wafer in the wafer-carrier head 20 so that the wafer is sandwiched between the carrier 20 and the polishing pad 28. Both the carrier and the polish platen 26 are rotatable during the polishing step. A primary slurry of cutting compound is applied to the surface of the polishing pad 28 during the primary polishing operation.
The secondary polishing station 18 is substantially the same as the primary polishing station 16 and likewise includes a trough 30 in which is disposed a second metal polish platen 32 having a polishing pad 34 mounted on its top surface. For polishing, the carrier 20 with the wafer held on its bottom surface is once again forced downwardly against the polishing pad 34. During the time of polishing, no vacuum is used to support the wafer-carrier head 20 so that the wafer is sandwiched between the carrier 20 and the polishing pad 34. Both the carrier 20 and the polish platen 32 are being rotated during the polishing step. A secondary slurry is applied to the surface of the polishing pad 34 during the secondary polishing operation.
However, the conventional polishing apparatus 10 has the disadvantage that each of the polish platens 26, 32 has a recess located in its center so as to allow access to certain hardware located below the respective platen for assembly, repair, and the like. Since the recesses in the platens are covered by the respective polishing pads 28, 34 applied to the top surfaces thereof, it was found that during the polish pad application air pockets would form in the recesses so as to cause bubbling due to the heating of the air trapped in the recesses and thereafter expanding. This heating and expansion of the trapped air will adversely affect the uniformity of the flatness in the polished wafers.
In current practice, the air pocket "bubble" problem created underneath the polishing pad is solved by a user through a cutting procedure such as with a razor blade. Each of the polishing pads is cut so as to form a slit in order to release any air expansion caused by the heating of the trapped air underneath the respective polishing pads which have been adhesively secured to the top surface of the metal polish platens in an air-tight manner. While this technique overcomes the problem of bubbling, it will create another setback due to the fact that the primary and secondary slurries applied during the polishing process will permeate the polishing pads through the cuts made and thus reduce the useful life of the polishing pads.
The present invention was made in view of this latter problem so as to eliminate the air pocket and reduce or remove any bubble formation without the need of cutting the polishing pads. As a result, the useful life of the polishing pads has been increased and therefore the manufacturing and labor costs have been reduced but yet the uniformity of flatness has still been maintained. Further, the overall CMP processing operation has been made more effective and efficient with greater dependability.